Since the beginning of the use of electrical devices and assemblies, particularly electronic devices such as computers, there has been the issue of Electro-Magnetic Interference (EMI) which can interfere with sensitive devices and receivers of Radio Frequency (R.F.) signals. EMI can degrade performance of devices that act as R.F. receivers such as computers and other electronic devices. Therefore, there is a need to prevent or minimize EMI leakage from the chassis or housing of the electrical device. As EMI can result in the interference or failure of other electrical devices or assemblies located nearby, the Federal Communications Commission (FCC) has established standards which severely limit the amount of permitted EMI emissions by electronic devices. As a result, there is the need for a means of shielding or eliminating as much of the EMI leakage as possible.
The present invention is an improvement over the previous EMI shielding devices in that a more effective and less expensive seal is created by forcing the planar surfaces of two members into face-to-face and continuous engagement, rather than using an intermittent or gapped seal, as in the prior art. The prior art which implements spring fingers in an attempt to prevent EMI leakage relies on the spring fingers as both a conductive grounding element to interconnect two cover portions electrically and to prevent the leakage. The prior art has not provided or indicated a satisfactory solution for EMI leakage through the gaps created by the spring fingers nor for a continuous and more effective seal without the need for the use of a gasket-like shields, which are fragile and easily damaged or complex shapes to trap the EMI emissions.
Ted Chuck, U.S. Pat. No. 4,789,570 discloses a metal grounding strip with a plurality of grounding spring fingers engaging a portion of a chassis side or lid on the lid edges to establish grounding contact. The grounding strip is partially ineffective to prevent the escape of EMI through the gaps between the chassis and chassis lid, due to the interdigital gaps.
Unlike the earlier devices, the present invention makes a continuous and more effective seal between the chassis base and the chassis lid without the use of a gasket-like shield, thereby eliminating the gap leakage and minimizing other EMI leakage while avoiding the problems associated with the gasket-like shields and open regions between elements of the chassis assembly.
A better and more complete understanding of the invention may be garnered from the drawings and detailed description of the preferred embodiment of the best mode of the invention as contemplated by the inventors.